Astronomers Discover Asteroid that Flies Close to the Sun

2021 PH27
An artist’s conception of asteroid 2021 PH27.
CTIO / NSF / NOIRLab / Aura / J. da Silva

There are new discoveries to be made, even in the interior solar system. This was highlighted this previous week with the announcement of the discovery of tiny asteroid 2021 PH27. The asteroid orbits the Sun in simply 113 days, the shortest orbital interval for any recognized asteroid and the second shortest orbital interval for any object in the solar system subsequent to the planet Mercury, at 88 days.

The discovery was made by astronomer Scott S. Sheppard (Carnegie Institution for Science) after looking by way of pictures taken by Ian Dell’Antonio and Shenming Fu (each Brown University) at night twilight on August 13, 2021. Subsequent observations with a number of telescopes round the world enabled astronomers to affirm the asteroid’s orbit.

2021 PH27
The orbit of asteroid 2021 PH27, displaying its place very close to aphelion and discovery.

The preliminary discovery observations have been made utilizing the Dark Energy Camera (DECam) primarily based at the National Science Foundation’s Blanco 4-meter telescope at the Cerro Tololo Inter-American Observatory (CTIO) advanced in Chile. Although the major mission for the Dark Energy Camera is the examine of cosmic growth, the Brown University astronomers agreed to use DECam at the starting of their observing run to take wide-field pictures in the fading twilight.

“The Dark Energy Camera on the NSF’s Blanco 4-meter telescope is one of the most powerful sky-survey imagers because of its large field of view — 2.2° wide, over four full Moons across — and the big telescope it is on,” says Sheppard. “Because of this, I thought it would be interesting to observe during twilight with this powerful instrument, to go fainter than anyone has before in this region of the solar system.”

Like fleeting Mercury, asteroids close to the Sun are sometimes bashful, showing close to the setting or rising Sun in twilight. Time on telescopes is usually in brief provide, and this discovery is a good instance of utilizing a survey already below way for multipurpose astronomy: Several astronomers agreed to interrupt their observing tasks to allow the asteroid hunt.

Dark Energy Survey (DES), Dark Energy Camera imager and CCDs at SiDet.
FNAL / DOE / DECam / CTIO / NOIRLab / R. Hahn / NSF / Aura 

“Telescope time for astronomers is very precious,” says Sheppard in a latest press release. “The international nature and love of the unknown make astronomers very willing to override their own science and observations to follow up new, interesting discoveries like this.”

Blanco 4-m scope
A view of the Víctor M. Blanco 4-meter Telescope at the Cerro Tololo Inter-American Observatory in Chile.
CTIO / NOIRLab / NSF / Aura / D. Munizaga

The Strange World of 2021 PH27

With a perihelion of simply 0.137 astronomical unit (a.u.) (20.4 million kilometers, or 12.7 million miles) and an aphelion of 0.785 a.u., 2021 PH27 is a member of the uncommon class of Atira asteroids, with orbits fully inside to Earth’s. Even at its closest method to our planet (close to the asteroid’s aphelion), 2021 PH27 passes a very good 0.215 a.u. from Earth. The asteroid additionally has the distinction of getting the smallest orbit of any recognized asteroid: With a semi-major axis of solely 0.46 a.u., 2021 PH27 beats out the former holder 2013 JX28 (semi-major axis of 0.6 a.u).

The asteroid has an absolute magnitude (its brightness at 1 a.u. away) of +17.7, suggesting it’s a couple of kilometer throughout. The floor of 2021 PH27 close to perihelion reaches a blistering 480°C (900°F). Like rock-comet 3200 Phaethon, 2021 PH27 is both a captured asteroid or dormant comet nucleus. With an orbital inclination of 31.7° relative to the ecliptic, 2021 PH27 passes shut to Venus occasionally; finally, the second planet from the Sun might modify the asteroid’s orbit or kick it out of the interior solar system fully. (Asteroids in the interior solar system are typically not everlasting company.)

2021 PH27
The movement of faint asteroid 2021 PH27.
Brown University / DECam

The closest passage of 2021 PH27 close to Venus for the coming decade shall be 0.019 a.u. (2.9 million kilometers) subsequent year on October 26, 2022. Keep in thoughts, although, that extra observations of 2021 PH27 are wanted to pin down its orbit: Astronomers have been fortunate to catch it simply after aphelion on August twelfth at a large 35° east of the Sun, and the subsequent favorable apparition isn’t till early 2022 at daybreak, two orbits from now. By that time, the IAU might give the object a proper identify, as nicely.

The discovery of 2021 PH27 is a tantalizing step in the direction of discovering doable members of an elusive class of hypothetical inter-Mercurial asteroids, referred to as Vulcanoids. The as-of-yet undiscovered class of asteroids takes its identify from Vulcan, a theoretical world inside to the orbit of Mercury evoked by Nineteenth-century astronomers to clarify the anomalous orbital precession of Mercury’s orbit. (Like Mercury, 2021 PH27 undergoes a large quantity of orbital precession, thanks to the gravitational panorama it traverses close to the Sun.) And although the introduction of Einstein’s normal relativity in the early twentieth century did away with the want for Vulcan to clarify precession, the concept that a population of tiny (smaller than 1 kilometer across) asteroids orbiting entirely interior to Mercury’s orbit has not been ruled out.

Unfortunately, the effort to nab the first true Vulcanoid can have to look ahead to future surveys past DECam. “The telescope elevation limits prevent us from observing objects interior to Mercury,” says Sheppard. “To date, looking for objects interior to Mercury has only been efficiently done through observations high up in Earth’s atmosphere from airplanes, from spacecraft in space, or during solar eclipse events.”

NASA’s Messenger spacecraft saved an digital eye out for Vulcanoids en route to Mercury, and NASA additionally scoured the area close to the Sun as a part of the mission to chase the 2017 complete solar eclipse with a pair of converted WB-57 bombers. Both surveys turned up empty.

2021 PH27 is an intriguing discovery, and should trace at extra to come.

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